1. Field of the Invention
The invention relates to a process to improve yields and reduce energy consumption in existing reactors for heterogeneous synthesis, and more particularly for the synthesis of ammonia, consisting of several catalytic beds through which synthesis gas flows axially, and cooled by feeding quench gas between beds.
2. Description of the Related Art
The invention also includes reactors so obtained.
It is known that one of the most common reactors currently used in ammonia synthesis plants is the type with four catalytic beds through which the synthesis gas flows axially, with intermediate quenching (Kellogg).
Numerous systems have been put forward, described and adopted in order to improve yields in the above-mentioned Kellogg reactors. More particularly, according to a description in "Nitrogen", Nr. 165, Jan./Feb. 1987, Topsoe Converted the Kellogg 4-bed reactor into a 2-bed reactor (by joining the 1st and 2nd bed and the 2nd and 3rd bed of the original reactor), with intermediate cooling between beds by means of a heat exchanger (FIG. 1 in the article quoted). The gas flows radially.
According to the same article, Kellogg themselves converted the reactor using the space in the 1st bed, introducing heat exchangers. The second bed in the existing reactor becomes therefore the 1st bed in the new layout according to which the 3rd and 4th bed in the existing reactor are intended to operate in parallel (according to the so-called split-flow system), and a reactor is therefore obtained in which there are two reaction stages with intermediate cooling by exchanger (FIG. 8 of the above-mentioned article). The gas flow remains axial as in the original reactor. Still in the above-mentioned article in "Nitrogen", it is stated that the applicants intend to maintain the same number of beds as in the original Kellogg reactor (4 beds) and the same quenching system between beds.
The gas flow is changed from axial to axial-radial (FIG. 4 in the article).
Ammonia Casale has been the first to describe a system for the conversion in situ of Kellogg reactors thus improving performance and reducing consumption. In effect in its U.S. Pat. No. 4,755,362 the Applicants show in FIG. 1A, as state of the Art, exactly the above classic Kellogg reactor with four axial beds and four intermediate quenches.
In this pioneering U.S. Pat. No. 4,755,362 the Applicants have maintained the same number of beds as at the start even in substantially radial reactors obtained by conversion in situ.
In Swiss Patent Application No. 02529/87-9 (corresponding to U.S. Pat. No. 4,963,338) the Applicants have suggested (FIG. 1) a further application of their system for modernizing a 4-bed Kellogg reactor converting it into a 3-bed reactor with quenching between the 1st and 2nd beds and cooling by means of an exchanger between the 2nd and 3rd beds. As the above-mentioned Figure shows, the 2nd bed in this layout is obtained by joining the 2nd and 3rd bed in the original reactor into a new 3-bed layout with quenching between the first and the second bed and an exchanger between the 2nd and 3rd bed. As FIG. 1 in said Swiss Patent Application shows, such Figure still being shown in this Patent Application, the 2nd and the 3rd bed were made into one with the interchanger being installed coaxially.
This solution, although offering considerable advantages when compared to the quench system, can however give rise to a less than optimal distribution of the catalyst, in the sense that the volume of catalyst installed in the second bed could result excessive.